Method of oxidizing asphalt flux with oxides of nitrogen



United States Patent 3,318,797 METHOD OF OXIDIZING ASPHALT FLUX WITH OXIDES OF NITROGEN Paul G. Campbell, Silver Spring, and James R. Wright,

Bethesda, Md., assignors to the United States of America as represented by the Secretary of Commerce No Drawing. Filed July 21, 1965, Ser. No. 473,878

2 Claims. (Cl. 208-6) ABSTRACT OF THE DISCLOSURE Asphalt flux is heated to 110-200 C. (230-392 F.) and blown with nitric oxide, nitrogen dioxide, or ultraviolet-irradiated nitrogen dioxide, diluted with air, nitrogen, etc.

Field of the invention This invention relates to methods of oxidizing asphalt flux, and more particularly to a method of oxidizing asphalt flux with oxides of nitrogen.

Description of the prior art Asphalt flux, which is the low-softening point residue obtained in the distillation of petroleum, is conventionally hardened or oxidized to hard commercial asphalts by air-blowing.- Typical air-blowing conditions are flux temperatures of 275-300 C., air flow rates of 30-50 cubic feet per ton-minute, and blowing times of -12 hours. As is well known, these conditions present a safety hazard, create air polution, and produce a thermally-degraded asphalt. However, prior attempts to moderate the conventional air-blowing conditions have not been economically-competitive, and therefore have not been widely adopted.

Summary of the invention Accordingly, an object of this invention is to provide a method of oxidizing asphalt flux which operates economically at moderate temperatures and gas flow rates.

Another object is to provide a method of oxidizing asphalt flux which produces a minimally thermally-degraded asphalt in a short time.

In accordance with the present invention, the asphalt flux to be oxidized is heated until it is fluid, and an oxide of nitrogen of this invention is blown therethrough. The rate of heating is adjusted to maintain the flux fluid, and the blowing is continued until the desired asphalt hardness is obtained. It is found that hard asphalts are formed in surprisingly short times, considering the low blowing temperatures used.

Description of the preferred embodiments 1 is not particularly useful, since it does not oxidize the flux substantialy faster than the air used in the conventional process.

Since the nitric oxide, nitrogen dioxide, and sensitized nitrogen dioxide used in this invention are powerful i from mixing nitrogen'dioxide and air.

oxidants, they preferably are diluted with other gases, to control the rate of oxidation of the fiLlX. Suitable diluents include nitrogen, oxygen, and air, of which air is preferred for economic reasons. The air diluent also contributes to the oxidation of the flux, thus reducing somewhat the amount of the selected oxide of nitrogen necessary to achieve a desired hardness of asphalt. The diluents are further useful in enabling one to establish blowing rates suflicient to vigorously agitate and circulate the heated flux, without exhausting to the atmosphere an excessive amount of unused oxide of nitrogen.

In accordance with this invention, the asphalt flux is heated to the minimum temperatures required to maintain the flux in a fluid state. At the beginning of the blowing operation, therefore, the flux is heated to about C. As the flux hardens through oxidation, the temperature of the flux is gradually raised, to a maximum of about 200 C. for the production of a hard coating or roofing asphalt. Flux temperatures higher than about 200 C. are not desirable, since they do not appreciably accelerate the oxidation of the flux, but merely tend to drive oif useful volatile oils in the flux, and otherwise thermally degrade the resulting asphalt. It is especially preferred to maintain the flux at about 110-175 C. during the blowing, which contributes greatly to the safety of the invention.

In the practice of this invention, the volume ratio of diluent gas to the selected oxide of nitrogen ranges from about 25:1 to 1:1. When the ratio of diluent gas to nitrogen oxide is greater than about 25:1, the blowing time is unduly increased; and when the ratio is less than about 1:1, the total flow rate must be cut back excessively, to prevent the loss of unused oxide of nitrogen. An especially preferred diluent to nitrogen ratio is about 20:1 to 5:1.

When nitrogen dioxide or nitrogen dioxide sensitized with ultraviolet radiation is selected for blowing the flux, the diluent gas preferably is mixed with the oxide, and the mixture blown through a single gas-inlet tube into the heated flux. If desired, however, the oxide and diluent may each be introduced separately into the flux, through a pair of gas-inlet tubes. In the latter case, the diluent gas inlet tube should be arranged with respect to the oxide inlet tube so as to disperse the oxide throughout the flux.

When nitric oxide is selected for blowing the flux, air is the preferred diluent. The air may be mixed with the nitric oxide, and the mixture blown into the flux through a single gas-inlet tube. In this case, however, the nitric oxide and air immediately react to form a mixture of nitrogen dioxide and air, similar to the mixture obtained Therefore, it is preferable to introduce the nitric oxide and the air simul taneously into the flux through separate tubes. When this is done, the nitric oxide and air, which are commingled with the heated flux, react in situ and produce an extremely rapid oxidation of the flux. The oxidation is much more rapid than the oxidation obtained when the nitric oxide and air are reacted prior to introduction into the asphalt. Hence it appears that the nitric oxide and air, reacting in the presence of the heated flux, produce an extremely reactive intermediate to nitrogen dioxide, and this intermediate rapidly oxides the flux. For this reason, it is preferable to introduce the nitric oxide and air simultaneously and separately in the flux.

In the present invention, the combined flow rates of the diluent gas and selected oxide of nitrogen are about 5-30 cubic feet per ton-minute. The flow rates are adjusted to thoroughly c-ommingle the gases with the heated flux, in accordance with the practice in the art.

At the low flux temperatures and moderate gas flow rates employed in this invention, one would ordinarily expect that the flux would have to be blown for an excessively long time, in order to produce a hard asphalt. By using the blowing gases of this invention, however, the blowing times required for the production of hard asphalts are made suprisingly short. By way of comparison, a typical asphalt flux of southeastern United States origin when heated to about 110175 C. and blown solely with air at a rate of about 30 cubic feet ton-minute requires about 90 hours of blowing to produce a coating grade asphalt having a ring-and-ball softening point of about 110 C. Using the same asphalt flux, flux temperature and gas flow rate, an asphalt softening point is obtained in about 4 /2 hours when the blowing gas consists of air and nitrogen dioxide in a volume ratio of about 10:1. Similarly, an asphalt of the same hardness is obtained in about 18 hours when the blowing gas consists of air and nitric oxide in a volume ratio of about 20: 1, the air and nitric oxide being introduced separately and simultaneously into the heated fiux. Thus, the blowing gases of the present invention accelerate the hardening of the asphalt flux at least fivefold over the hardening provided by air alone.

Since in the present invention the flux is maintained at about 110175 C. during the blowing, the resultant asphalts are thermally-degraded a minimum amount. Consequently, the asphalts are outstandingly durable, which can more than offset the added cost of the oxides of the nitrogen. Additional benefits realized by the use of the low temperatures of this invention are that the process is relatively free from the hazards of fire and explosion, and may readily be designed as a continuous rather than batch operation.

The reasons for the rapid hardening of the asphalt flux at the low temperatures of this invention are not fully understood. Without intending to limit the invention, it is suggested that the hardening is due to one or more of the following factors: (1) some thermal dissociation of the oxides of nitrogen in the presence of the heated flux, (2) the oxides of nitrogen per se, (3) a reactive dissociation complex, or (4) a more reactive form of oxygen.

The following examples further illustrate the invention.

Example I.A small amount of an asphalt flux of southeastern US. origin having a softening point of about 40 C. was heated to about 110 C. and blown with a mixture of air nitrogen dioxide in a volume ratio of about 10:1 and at a rate of about 30 cubic feet per tonminute. The temperature of the flux was gradually increased over hours to about 160 C., after which time the ring-and-ball softening point of the resultant asphalt was about 112 C.

Example II.--Using the same flux, temperatures and gas flow rates as in Example I, air and nitric oxide in a volume ratio of about 20:1 were introduced separately and simultaneously into the heated flux. The softening point after 12 hours was about 82 C.

Example III.-Using the same flux and procedure as in Example I, the fiux was blown with a mixture of nitrogen and nitrogen dioxide in a volume ratio of about 5:1. The softening point of the flux increased to about 86 C. in 4 hours.

Example IV.Using the same flux, gases and procedure as in Example III, the volume ratio was changed to 10:1. In 4 hours the softening point of the resultant asphalt was about C.

Example V.Using the same flux and procedure as in Example I, the flux was blown with a mixture of nitrogen and ultraviolet sensitized nitrogen dioxide in a volume ratio of about 10:1, causing the flux to harden to a softening point of about 94 C. in 5 hours.

It will be obvious to those skilled in the art that the above specific illustrative embodiments may be modified without departing from the scope and spirit of the invention. For example, it will be readily apparent that the process of this invention may be used to prepare asphalts in any grade intermediate to the hard coating or roofing grade asphalts. The intermediate asphalts may further be used to prepare laminates, rubber compounds and the like, in the manner well known in the art. Accordingly, it is intended that the invention not be limited to the details of illustration, but only as defined in the appended claims.

What is claimed is:

1. The metod of oxidizing asphalt flux which comprises,

(a) heating said fiux to about C.,

(b) blowing said heated flux simultaneously with a diluent gas and a gas selected from the group consisting of nitric oxide, nitrogen dioxide, and nitrogen dioxide sensitized with ultraviolet radiation, in a diluent to oxide volume ratio of about 20: 15:l, at a blowing rate of about 530 cubic feet per tonminute,

(c) maintaining said blowing while gradually increasing said flux temperature to about C. over a period of about 4-18 hours, and

(digl discontinuing said heating and blowing of said 2. The method set forth in claim 1, wherein said diluent gas is air and said selected gas is nitric oxide, said nitric oxide and air being blown separately as well as simultaneously into said flux.

References Cited by the Examiner UNITED STATES PATENTS 1,057,227 3/1913 Dubbs 2086 1,912,667 6/1933 Swerissen 2084 2,148,869 2/1939 McConnell 2084 3,258,419 6/1966 Hanson 20844 FOREIGN PATENTS 25,912 4/ 1931 Australia.

DANIEL E. WYMAN, Primary Examiner.

P. E. KONOPKA, Assistant Examiner. 

1. THE METHOD OF OXIDIZING ASPHALT FLUX WHICH COMPRISES, (A) HEATING SAID FLUX TO ABOUT 110*C., (B) BLOWING SAID HEATED FLUX SIMULTANEOUSLY WITH A DILUENT GAS AND A GAS SELECTED FROM THE GROUP CONSISTING OF NITRIC OXIDE, NITROGEN DIOXIDE, AND NITROGEN DIOXIDE SENSITIZED WITH ULTRAVIOLET RADIATION, IN A DILUENT OT OXIDE VOLUME RATIO OF ABOUT 20:1-5:1, AT A BLOWING RATE OF ABOUT 5-30 CUBIC FEET PER TONMINUTE, (C) MAINTAINING SAID BLOWING WHILE GRADUALLY INCREASING SAID FLUX TEMPERATURE TO ABOUT 175*C. OVER A PERIOD OF ABOUT 4-1, HOURS, AND (D) DISCONTINUING SAID HEATING AND BLOWING OF SAID FLUX. 